WASHINGTON -- To meet the body's daily energy and nutritional needs while minimizing risk for chronic disease, adults should get 45 percent to 65 percent of their calories from carbohydrates, 20 percent to 35 percent from fat, and 10 percent to 35 percent from protein, says the newest report on recommendations for healthy eating from the National Academies' Institute of Medicine. To maintain cardiovascular health at a maximal level, regardless of weight, adults and children also should spend a total ofat least one hour each day in moderately intense physical activity, which is double the daily minimum goal set by the 1996 Surgeon General's report.

Because carbohydrates, fat, and protein all serve as energy sources and can substitute for one another to some extent to meet caloric needs, the recommended ranges for consuming these nutrients should be useful and flexible for dietary planning. Earlier guidelines called for diets with 50 percent or more of carbohydrate and 30 percent or less of fat; protein intake recommendations are the same. The new acceptable ranges for children are similar to those for adults, except that infants and younger children need a slightly higher proportion of fat -- 25 percent to 40 percent of their caloric intake, said the panel that wrote the report.

"We established ranges for fat, carbohydrates, and protein because they must be considered together," said panel chair Joanne Lupton, professor of nutrition, Texas A&M University, College Station. "Studies show that when people eat very low levels of fat combined with very high levels of carbohydrates, high-density lipoprotein concentration, or 'good' cholesterol, decreases. Conversely, high-fat diets can lead to obesity and its complications if caloric intake is increased as well, which is often the case. We believe these ranges will help people make healthy and more realistic choices based on their own food preferences."

The report stresses the importance of balancing diet with physical activity, recommending total calories to be consumed by individuals of given heights, weights, and genders for each of four different levels of physical activity. For example, a 30-year-old woman who is 5 feet 5 inches tall and weighs 111 to 150 pounds should consume between 1,800 and 2,000 calories daily if she lives a sedentary lifestyle. However, if she is a very active person, her recommended total caloric intake increases to 2,500 to 2,800 calories per day. If her lifestyle fits the moderately active category as defined in the report, which is the minimum level of activity to decrease risk of chronic disease, she should eat between 2,200 and 2,500 calories daily. Using grams for the recommended ranges of intake, she should consume 55 to 97 grams of fat and 285 to 375 grams of carbohydrates per day.

The new one-hour-a-day-total activity goal stems from studies of how much energy is expended on average each day by individuals who maintain a healthy weight. Energy expenditure is cumulative, including both low-intensity activities of daily life, such as stair climbing and housecleaning, and more vigorous exercise like swimming and cycling. Someone in a largely sedentary occupation can achieve the new exercise goal by engaging in a moderate-intensity activity, such as walking at 4 miles per hour, for a total of60 minutes every day, or engaging in a high-intensity activity, such as jogging for 20 to 30 minutes four to seven days per week.

New Dietary Recommendations

Since the publication of the Recommended Dietary Allowances in 1989 and the Canadian Recommended Nutrient Intakes in 1990, new information has emerged about nutrient requirements that warrants the development of updated guidelines. This report, the sixth in a series, develops new guidelines for the United States and Canada for the consumption of energy, carbohydrates, fiber, fat, fatty acids, cholesterol, protein, and amino acids, collectively known as macronutrients.

In the past, recommended dietary allowances or RDAs have served as the benchmarks of nutritional adequacy in the United States. The new Dietary Reference Intakes, or DRIs, are established using an expanded concept that includes indicators of good health and the prevention of chronic disease, as well as possible adverse effects of overconsumption. The panel assessed thousands of scientific studies linking excessive or inadequate consumption of fats, carbohydrates, and protein with increased risk for dietary deficiency diseases, obesity, heart disease, diabetes, and other chronic illnesses. The DRIs include not only recommended intakes, intended to help individuals meet their daily nutritional requirements, but also tolerable upper intake levels (ULs) that help them avoid harm from consuming too much of a nutrient.

The DRIs are designed to meet the needs of individuals who are healthy and free ofspecific diseases or conditions that may alter their daily nutritional requirements. It is expected that people known to have specific conditions or chronic diseases will get nutritional advice from their health professionals that is tailored to their special needs.

Concern AboutAdded Sugars

Both children and adults should consume at least 130 grams of carbohydrates each day, the report says. However, this newly set RDA is based on the minimum amount of carbohydrates needed to produce enough glucose for the brain to function, and most people regularly consume far more.

The report suggests thatadded sugars should comprise no more than 25 percent of total calories consumed. Distinguished from natural sugars, such as lactose found in milk and fructose found in fruits, added sugars are those incorporated into foods and beverages during production. Major sources include candy,soft drinks, fruit drinks, pastries, and other sweets. The suggested maximum level stems from the evidence that people whose diets are high in added sugars have lower intakes of essential nutrients.

Are All Fats Bad?

Fat is a major source of energy for the body and aids in the absorption of essential vitamins. Some foods that are major contributors of fat in the diet include butter, margarine, vegetable oils, visible fat on meat and poultry, whole milk, egg yolks, and nuts. High-fat diets usually mean increased intakes of saturated fat, which can raise the amount of low-density lipoprotein and the level of "bad" cholesterol in the bloodstream of some individuals and heightens their risk for heart disease. Meats, baked goods, and full-fat dairy products are the main sources of saturated fat in most diets. Because saturated fat and cholesterol provide no known beneficial role in preventing chronic diseases, they are not required at any level in the diet, the report says. Recognizing that completely eliminating saturated fat and cholesterol from the typical diet in the United States or Canada would make it very difficult to meet other nutritional guidelines, the panel recommended keeping consumption as low as possible while maintaining a nutritionally adequate diet.

Monounsaturated and polyunsaturated fatty acids, also present in fat, reduce blood cholesterol levels and thus lower the risk of heart disease when they replace saturated fats in the diet. People must get two types of polyunsaturated fatty acids, known as alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid), from the foods they consume since neither is synthesized in the body. A lack of either one will result in symptoms of deficiency, including scaly skin and dermatitis, although these deficiencies are extremely rare in the United States and Canada. The report sets recommended intakes for linoleic acid, present in high levels in vegetable oils such as safflower oil or corn oil, at 17 grams per day for men and 12 grams per day for women based on average intakes in the United States. For alpha-linolenic acid, found in milk and some vegetable oils such as soybean and flaxseed oils, the recommendations are 1.6 and 1.1 grams per day for men and women, respectively.

Partially hydrogenated vegetable oils, such as those used in many margarines and shortenings, contain a particular form of unsaturated fat known as trans fatty acids. Trans fatty acids have physical properties generally resembling saturated fatty acids, and their presence tends to harden oils. The report's findings and recommendations on trans fatty acids were released in early July at the request of the Food and Drug Administration as an important step in its process to determine whether trans fat should be listed on nutrition labels. Often found in cookies, crackers, dairy products, meats, and fast food, trans fatty acids increase the risk of heart disease by boosting levels of bad cholesterol. Because they are not essential and provide no known health benefit, there is no safe level of trans fatty acids and people should eat as little of them as possible while consuming a nutritionally adequate diet. Because trans fatty acids occur in so many types of food, an all-out ban is impractical and would make it extremely difficult to get a nutritionally adequate diet, the panel added.

New Facts on Fiber

The report contains the first recommended intake levels for fiber from the Food and Nutrition Board. The fiber recommendations are based on studies that show an increased risk for heart disease when diets low infiber are consumed. Although there is some evidence to suggest that fiber in the diet may also help to prevent colon cancer and promote weight control, the data are inconclusive at this point. The recommended daily intake for total fiber for adults 50 years and younger is set at 38 grams for men and 25 grams for women, while for men and women over 50 it is 30 and 21 grams per day, respectively, due to decreased consumption of food. The report also provides recommended intakes for children and teenagers. Many new food products are marketed as containing fiber, but the lack of a uniform definition of fiber for regulatory purposes casts doubts on the usefulness ofsome content claims. Therefore, the report provides a specific definition of what should be called fiber in food. It defines "total fiber" as the combination of "dietary" and "functional" fiber. Dietary fiber is the edible, nondigestible component of carbohydrates and lignin naturally found in plant food. Some foods with dietary fiber include cereal bran, flaked corn cereal, sweet potatoes, legumes, and onions. Functional fiber refers to those fiber sourcesthat are shown to have similar health benefits as dietary fiber, but are isolated or extracted from natural sources or are synthetic. An example would be pectin extracted from citrus peel and used as a gel that is the basis for jams and jellies. The definition of functional fiber aims to exclude fiber-like products, whether extracted or synthesized, that cannot be shown to have proven health benefits. It is hoped that regulatory bodies in both the United States and Canada will work toward adopting these definitions.

Recommended Levels for Protein

The report establishes age-based requirements for the first time for all nine of the essential amino acids found in dietary protein. Values are included for pregnant women, infants, and children based on their special needs. Using new data,the report reaffirms previously established recommended levels of protein intake, which is 0.8 grams per kilogram of body weight for adults. Recommended intake of protein during pregnancy also is increased.Because data on the potential for high-protein diets to produce chronic or other diseases are often conflicting or inadequate, tolerable upper intake levels for consumption could not be determined for protein or for the individual amino acids. However, given the lack of data on overconsumption for some of these amino acids and protein, caution is warranted in consuming levels significantly above those normally found in foods.

This study was sponsored by the U.S. Department of Health and Human Services Office of Disease Prevention and Health Promotion; Health Canada; U.S. Food and Drug Administration; National Institutes of Health; Centers for Disease Control and Prevention; U.S. Department of Agriculture; U.S. Department of Defense; Institute of Medicine; the Dietary Reference Intakes Private Foundation Fund, including the Dannon Institute and the International Life Sciences Institute-North America; and the Dietary Reference Intakes Corporate Donors' Fund, contributors to which include Roche Vitamins Inc., Mead Johnson Nutrition Group, and M&M Mars.

The study was undertaken by scientists from the United States and Canada under the auspices of the Institute of Medicine's Food and Nutrition Board, which has been responsible for developing RDAs for United States for the last 60 years. The Institute of Medicine is a private, nonprofit organization that provides health policy advice under a congressional charter granted to the National Academy of Sciences.